WEBVTT - Navigation in Spaaaace 0:00:00.720 --> 0:00:03.680 Hey there, listeners, this is Jonathan. Before we get into 0:00:04.280 --> 0:00:09.520 the episode, I want to acknowledge something. Uh. Twitter user 0:00:09.960 --> 0:00:14.920 Charlie Tango Bravo helpfully pointed out that I made a mistake. 0:00:15.120 --> 0:00:19.080 When we first published this episode, I completely misrepresented the 0:00:19.200 --> 0:00:23.400 inverse square law, and so later in this episode you 0:00:23.480 --> 0:00:29.160 will hear me kind of interrupt to give a proper explanation. 0:00:29.680 --> 0:00:33.760 My apologies for that. Uh and um, yeah, I mean, 0:00:34.640 --> 0:00:37.920 this one's totally on me. I made a mistake, and 0:00:38.280 --> 0:00:42.000 I feel real dumb about it. But you know, mistakes happen. 0:00:42.880 --> 0:00:45.040 It doesn't. It just tells me I need to be 0:00:45.440 --> 0:00:48.320 even more careful in the future to make sure that 0:00:48.440 --> 0:00:52.479 I'm not misrepresenting something, which I totally was in the 0:00:52.520 --> 0:00:56.080 original version of this episode. Anyway, let's get to the episode, 0:00:56.280 --> 0:00:58.600 and when we get to the part where I'll correct it, 0:00:58.960 --> 0:01:08.199 I'm pretty sure we'll be apparent. Enjoy. Welcome to Tech Stuff, 0:01:08.440 --> 0:01:15.760 a production from I Heart Radio. Hey there, and welcome 0:01:15.800 --> 0:01:18.880 to tech Stuff. I'm your host, Jonathan Strickland. I'm an 0:01:18.920 --> 0:01:21.840 executive producer with I Heart Radio and I love all 0:01:21.920 --> 0:01:27.400 things tech and listener Terry A. Carlson, and I apologize 0:01:27.440 --> 0:01:32.040 for very likely Butchering your name, asked if I might 0:01:32.120 --> 0:01:35.640 cover how space vehicles navigate. So we're going to talk 0:01:35.680 --> 0:01:38.399 about navigation, and this is one of those things I 0:01:38.440 --> 0:01:44.360 find really fascinating and also sometimes frequently actually a bit confusing. 0:01:44.760 --> 0:01:47.680 Now I blame part of that confusion on my own 0:01:47.760 --> 0:01:51.120 fascination with stuff like Star Wars, which some folks call 0:01:51.200 --> 0:01:53.960 science fiction. I think of it as fantasy that happens 0:01:53.960 --> 0:01:57.240 to be set in space, or even Star Trek, which 0:01:57.640 --> 0:01:59.960 is closer to science fiction than Star Wars, but can 0:02:00.080 --> 0:02:03.440 play a bit fast and loose with science and technology. 0:02:03.680 --> 0:02:06.200 And these kind of properties gave me a really cool 0:02:07.000 --> 0:02:10.720 but an accurate feel for how space navigation works. Terry, 0:02:10.760 --> 0:02:15.560 you asked that I cover what references and methods do 0:02:15.639 --> 0:02:19.839 space programs used to actually do space navigation? And that's 0:02:19.840 --> 0:02:23.000 a great question, because all of this really does rely 0:02:23.320 --> 0:02:29.200 on reference or relationships between a vehicle and something else, 0:02:29.760 --> 0:02:32.600 Like it's all relative. You know, we're going to talk 0:02:32.639 --> 0:02:35.240 about that a lot in this episode. And I guess 0:02:35.840 --> 0:02:39.200 on some level this is intuitive, but I had not 0:02:39.320 --> 0:02:44.320 really thought about it in concrete terms before. So, for example, 0:02:44.800 --> 0:02:47.840 here on Earth, if you're giving directions to someone, you 0:02:47.880 --> 0:02:50.080 would tell that person how to get to a place 0:02:50.560 --> 0:02:54.120 relative to where they are right now, Right, I mean, 0:02:54.120 --> 0:02:56.920 the same thing holds true for space vehicles. But we've 0:02:56.919 --> 0:03:00.120 got to remember that everything in space is moved ing 0:03:00.720 --> 0:03:05.520 all the time. So here on Earth, if you need directions, 0:03:05.520 --> 0:03:08.080 you can start from a position in which you know 0:03:08.200 --> 0:03:10.960 you're not moving relative to the Earth. You're standing still. 0:03:11.080 --> 0:03:14.440 On Earth, You're still moving, but that's because the arts moving. 0:03:14.680 --> 0:03:18.119 We're going to get to that. And you know you're 0:03:18.160 --> 0:03:21.000 standing still with reference to the Earth. But in space, 0:03:21.120 --> 0:03:24.360 everything is moving in reference to everything else. Now you 0:03:24.360 --> 0:03:28.280 could be moving at a similar velocity relative to your surroundings. 0:03:28.520 --> 0:03:31.800 So from your perspective, it might seem like you're not 0:03:31.840 --> 0:03:35.560 all really moving together, but trust me, you totes are. 0:03:36.400 --> 0:03:39.400 Now what I'm about to go into it really matters 0:03:39.560 --> 0:03:43.040 when we start thinking about the possibility of traveling beyond 0:03:43.040 --> 0:03:46.080 our solar system to another. But it's it's, you know, 0:03:46.160 --> 0:03:48.440 something that we have to take into consideration, even when 0:03:48.440 --> 0:03:52.320 we're talking about travel within our Solar system. So let's 0:03:52.320 --> 0:03:54.760 start with the easiest stuff first and then work our 0:03:54.800 --> 0:03:59.120 way up. The Earth travels in a nearly circular orbit 0:03:59.200 --> 0:04:02.000 around the Sun, right, I mean, this is not news 0:04:02.000 --> 0:04:05.360 to you. I imagine. So the Earth is moving, it's 0:04:05.400 --> 0:04:08.600 moving in an orbital path around the Sun. The orbit 0:04:08.920 --> 0:04:12.240 moves at a speed that's around sixty thousand miles per 0:04:12.280 --> 0:04:16.960 hour if you prefer, that's about or almost thirty kilometers 0:04:17.000 --> 0:04:20.920 per second. Now, if we're talking about going to space 0:04:21.000 --> 0:04:24.000 to do stuff in low Earth orbit, we're pretty much 0:04:24.040 --> 0:04:27.040 thinking to Earth, right, We're not too worried about everything 0:04:27.080 --> 0:04:30.680 else that's going on. The orbital speed of Earth isn't 0:04:30.720 --> 0:04:32.920 as big a deal in that case, we don't have 0:04:32.960 --> 0:04:36.520 to take that into as much account. But let's say 0:04:36.520 --> 0:04:39.480 that we want to travel to Mars. Go from Earth 0:04:39.560 --> 0:04:42.559 to Mars. Well, Mars is further out from the Sun 0:04:42.560 --> 0:04:46.679 than Earth, right, I mean it goes my very educated mother. 0:04:46.960 --> 0:04:51.159 So Mars comes after Earth. Oh, in case you've not 0:04:51.279 --> 0:04:55.080 actually heard that mnemonic device, this is how I learned it. 0:04:55.080 --> 0:05:01.000 It was my very educated mother just served us nine pickles. 0:05:01.440 --> 0:05:07.919 That stands for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, 0:05:08.000 --> 0:05:11.680 and Pluto the planets except well, you know, when I 0:05:11.720 --> 0:05:13.839 was a kid, Pluto was a planet, and then Pluto 0:05:13.960 --> 0:05:15.760 kind of got the boot as far as being a 0:05:15.800 --> 0:05:18.680 planet goes. So I guess now you could say, my 0:05:18.880 --> 0:05:24.640 very educated mother just served us nothing. Thanks mom. Okay. So, 0:05:24.960 --> 0:05:28.800 Mars is further out from the Sun than Earth is, 0:05:29.360 --> 0:05:33.359 and Mars's orbit is obviously a bigger circle around the 0:05:33.440 --> 0:05:36.240 Sun than Earth's orbit is, because you know, Mars is 0:05:36.440 --> 0:05:39.599 further out from the center of our solar system. Mars 0:05:39.640 --> 0:05:44.000 also doesn't have the same orbital velocity as Earth. Earth 0:05:44.040 --> 0:05:47.120 completes one orbit of the Sun every three sixty five 0:05:47.200 --> 0:05:49.720 Earth days, with a little bit of change leftover. That's 0:05:49.760 --> 0:05:52.560 why we have to have leap years, and Mars's orbit 0:05:52.720 --> 0:05:56.080 is just a hair under six hundred eighty seven Earth 0:05:56.160 --> 0:06:00.839 days long. But beyond that, Mars's orbital velocity is closer 0:06:00.880 --> 0:06:04.320 to twenty kilometers per second. Remember Earth's is closer to 0:06:04.520 --> 0:06:08.159 thirty kilometers per second. So Mars is not just moving 0:06:08.440 --> 0:06:11.800 in a greater distance because it's orbit is larger, it's 0:06:11.839 --> 0:06:15.040 moving a little slower compared to Earth, you know, and 0:06:15.360 --> 0:06:18.560 again relative to the Sun. So that means if we 0:06:18.640 --> 0:06:21.760 want to plot a course from Earth to Mars, we 0:06:21.800 --> 0:06:25.640 have to take all that into account, right, because we 0:06:25.720 --> 0:06:28.880 can't travel instantaneously. It takes time for us to get 0:06:28.920 --> 0:06:31.760 from point A to point B. We can't just point 0:06:31.760 --> 0:06:34.640 a rocket at where Mars appears to be to us 0:06:35.120 --> 0:06:37.960 right at that moment and then launch the rocket in 0:06:38.000 --> 0:06:41.120 that direction. You know, look at the sky, find the 0:06:41.160 --> 0:06:44.600 red dot and say aim that away, because you know, 0:06:44.760 --> 0:06:47.719 the positions of Earth and Mars are shifting in their orbits, 0:06:47.800 --> 0:06:50.520 and Mars will not be at that same spot by 0:06:50.520 --> 0:06:53.240 the time the vehicle we launch gets there. Heck, it's 0:06:53.279 --> 0:06:55.920 not even at that spot as we look at it, 0:06:56.000 --> 0:06:59.560 because it takes time for light to travel from Mars 0:06:59.600 --> 0:07:02.800 back to us, So we're really looking at where Mars 0:07:03.120 --> 0:07:05.760 used to be, and we would be shooting a rocket 0:07:06.000 --> 0:07:09.720 at where Mars used to be a really long time ago. Uh. 0:07:09.760 --> 0:07:13.400 The vehicle it would take months to travel there, so 0:07:13.520 --> 0:07:15.760 by the time it would get to that position in space, 0:07:16.280 --> 0:07:18.880 Mars wouldn't be there anymore. By the way, all this 0:07:19.000 --> 0:07:21.680 orbital stuff is why when we talk about sending a 0:07:21.840 --> 0:07:25.800 crew of human astronauts to Mars, we talk about missions 0:07:25.840 --> 0:07:28.720 that typically are on the order of a couple of 0:07:28.800 --> 0:07:32.720 years in length. The trip from Earth to Mars could 0:07:32.760 --> 0:07:35.880 take around eight months, and that's if we time it 0:07:35.960 --> 0:07:40.440 so that the launch vehicle UH shoots the spacecraft up 0:07:40.480 --> 0:07:43.400 and has the spacecraft travel the least amount of distance 0:07:44.040 --> 0:07:47.320 needed in order to go from Earth to Mars. That 0:07:47.360 --> 0:07:49.880 means you're timing it right. You're aiming at where Mars 0:07:50.000 --> 0:07:52.000 is going to be, and you want to time it 0:07:52.480 --> 0:07:55.320 so that Earth and Mars are at one of the 0:07:55.360 --> 0:07:59.760 closest points in their respective orbits to one another. You 0:08:00.000 --> 0:08:02.360 out of time it just right. And because of the 0:08:02.360 --> 0:08:04.960 difference in orbital velocities and the fact that mars Is 0:08:05.040 --> 0:08:08.320 year is significantly longer than Earth's year, that means that 0:08:08.360 --> 0:08:11.840 by the time you would arrive on Mars, Earth and 0:08:11.880 --> 0:08:14.880 Mars would no longer be super close together anymore. Right 0:08:15.000 --> 0:08:18.360 Like they're they're constantly in motion, so now they're moving 0:08:18.400 --> 0:08:21.520 apart from each other. That means for you to get 0:08:21.560 --> 0:08:24.400 back to Earth, you would need way more fuel for 0:08:24.440 --> 0:08:27.520 your return trip than you did for your trip out 0:08:27.560 --> 0:08:31.120 to Mars. Potentially, so the most fuel efficient thing to 0:08:31.160 --> 0:08:34.720 do is to hunker down on Mars and do all 0:08:34.760 --> 0:08:37.880 your science e stuff and you wait for the planets 0:08:37.920 --> 0:08:40.920 to reach a point in their orbits where again you 0:08:40.960 --> 0:08:43.320 will be traveling the least amount of distance you can 0:08:43.360 --> 0:08:46.480 get away with. And all told, that means a mission 0:08:46.520 --> 0:08:49.800 needs to last around two years to get all that done. 0:08:49.960 --> 0:08:52.960 Plus you know, theoretically you could even spend some of 0:08:52.960 --> 0:08:55.480 that time on Mars making rocket fuel, so you wouldn't 0:08:55.520 --> 0:08:57.680 necessarily have to carry all of it with you on 0:08:57.760 --> 0:09:00.960 the way there. Anyway, that's just a simple example of 0:09:01.000 --> 0:09:05.839 how motion in space matters. But we're just getting started, right, 0:09:05.880 --> 0:09:08.960 So I've touched on stuff like low Earth orbit and 0:09:09.080 --> 0:09:13.320 interplanetary travel within a solar system. But it's not just 0:09:13.480 --> 0:09:17.080 that the planets are moving around the Sun. Our entire 0:09:17.360 --> 0:09:21.760 Solar system is hurtling through space. We are part of 0:09:21.760 --> 0:09:24.200 the Milky Way Galaxy, and at the center of the 0:09:24.240 --> 0:09:27.880 Milky Way Galaxy there is a super massive black hole 0:09:28.520 --> 0:09:31.880 that's kind of the you know, it's like the Sun 0:09:32.000 --> 0:09:34.760 is in our Solar system, except there's a supermassive black 0:09:34.760 --> 0:09:38.920 hole in the middle of a galaxy billions of solar systems. 0:09:38.960 --> 0:09:43.000 Scientists estimate that our galaxy has somewhere between a hundred 0:09:43.040 --> 0:09:48.000 to four hundred billion stars in it. So think about that. 0:09:48.080 --> 0:09:51.079 I can't. I tried, but that's just a number that's 0:09:51.120 --> 0:09:53.600 just way too big for me to even get a 0:09:53.679 --> 0:09:57.880 rudimentary grasp on it. Anyway, our solar system is traveling 0:09:57.920 --> 0:10:00.600 in its orbit in the galaxy at a speed of 0:10:00.640 --> 0:10:05.480 around four thousand miles per hour or two kilometers per second. 0:10:06.000 --> 0:10:09.439 Then we have to consider that our galaxy is also 0:10:09.480 --> 0:10:13.079 in motion. We've got other neighboring galaxies in our neighborhood 0:10:13.160 --> 0:10:16.120 is just part of a super cluster of galaxies, and 0:10:16.200 --> 0:10:20.080 that in itself is part of an even bigger super cluster. 0:10:20.640 --> 0:10:23.400 And we're all hurtling through space at around a thousand 0:10:23.480 --> 0:10:27.760 kilometers per second. Where are we going? Well, I mean, 0:10:27.800 --> 0:10:30.080 I want to say, get in loser, we're going shopping, 0:10:30.280 --> 0:10:35.080 but we're not. We're headed to the Great Attractor. And 0:10:35.120 --> 0:10:38.760 to my surprise, that isn't Oscar Isaac. It's a gravitational 0:10:38.840 --> 0:10:44.320 point in the Lania Kia super cluster. Uh. And um, 0:10:44.400 --> 0:10:48.079 you know the Great Attractor is also moving towards another mass, 0:10:48.160 --> 0:10:53.480 the Shapley super Cluster. I guess there's always a bigger fish. 0:10:53.559 --> 0:10:56.040 And you know, we could keep going down this rabbit hole. 0:10:56.080 --> 0:10:57.720 But what I really wanted to point out is that 0:10:57.720 --> 0:11:00.920 we're talking about a lot of body ease in motion here, 0:11:00.960 --> 0:11:03.840 and that makes navigation more tricky, right, I mean, this 0:11:03.920 --> 0:11:06.360 is kind of like saying that you stop to ask 0:11:06.400 --> 0:11:09.800 for directions, but the town you stop in is actually 0:11:09.840 --> 0:11:12.240 moving on the map, and the place you're going to 0:11:12.400 --> 0:11:15.600 is also moving on the map. Maybe it's moving away 0:11:15.760 --> 0:11:18.960 from the town you are in, which is still in motion. 0:11:19.200 --> 0:11:21.160 So the route you are going to take to get 0:11:21.160 --> 0:11:24.439 there is changing by the minute. It gets complicated, so 0:11:24.640 --> 0:11:28.040 you have to take, uh, you know, into account a 0:11:28.080 --> 0:11:30.679 lot of things. You have to take reference points in 0:11:30.760 --> 0:11:33.360 order to make it all makes sense. And of course 0:11:33.400 --> 0:11:36.480 that's like talking about a map that's two dimensional. Obviously 0:11:36.480 --> 0:11:40.120 in space you're talking about three dimensional. You're not limited 0:11:40.400 --> 0:11:44.720 by a two dimensional plane. You're moving in three dimensional space. This, 0:11:44.880 --> 0:11:47.880 by the way, is all before we even consider stuff 0:11:47.920 --> 0:11:53.680 like relativity, which makes things even more weird. Einstein's theories 0:11:53.720 --> 0:11:57.360 of relativity really show how our universe behaves in ways 0:11:57.400 --> 0:12:02.000 that we don't often get to observe of directly. So 0:12:02.280 --> 0:12:05.440 we don't have a lot of direct perspective on these things. 0:12:05.720 --> 0:12:09.559 But let's use an example to explain some of relativity, 0:12:09.640 --> 0:12:13.000 and we'll start with special relativity. That's the I would 0:12:13.040 --> 0:12:16.480 argue the easier of the two to get a grasp on. Alright, 0:12:16.520 --> 0:12:19.880 so we've got two people and we're gonna name them 0:12:19.920 --> 0:12:25.000 Alice and Bob. Alice has superpowers, and Alice can travel 0:12:25.120 --> 0:12:28.360 through space without a space suit and can move at 0:12:28.440 --> 0:12:31.480 near the speed of light. So she flies through space 0:12:31.920 --> 0:12:34.320 close to the speed of light, and she goes and 0:12:34.360 --> 0:12:37.360 flies off on an adventure at top speed. When she 0:12:37.400 --> 0:12:40.280 comes back and she meets up with her best friend Bob, 0:12:40.760 --> 0:12:44.360 the two notice something unusual. So to Alice, it'll seem 0:12:44.400 --> 0:12:49.320 like Bob aged faster than normal, as if more time 0:12:49.440 --> 0:12:53.280 had passed for Bob than it did for Alice. To Bob, 0:12:53.640 --> 0:12:56.960 it will seem like Alice has aged less than normal, 0:12:57.440 --> 0:13:00.400 like not as much time passed for her, like like 0:13:00.400 --> 0:13:04.120 like less time pass less than it should have. And 0:13:04.160 --> 0:13:07.959 the reason for this is that the faster your speed 0:13:08.200 --> 0:13:11.600 is relative to some other reference point. This is why 0:13:11.640 --> 0:13:14.920 we talk about relativity. It is relative to some other 0:13:14.960 --> 0:13:19.040 reference point, the slower time will pass for you relative 0:13:19.080 --> 0:13:22.839 to that reference point. So again, like Bob is our 0:13:23.000 --> 0:13:28.400 our reference point for Alice. So it appears like, you know, 0:13:29.720 --> 0:13:32.960 Alice hasn't aged as much because time appeared to pass 0:13:32.960 --> 0:13:36.720 slower for Alice than it did to Bob. Now to Alice, 0:13:37.320 --> 0:13:40.040 time will have seemed to pass as normal for our 0:13:40.080 --> 0:13:42.640 own frame of reference. So in other words, it wouldn't 0:13:42.720 --> 0:13:45.600 feel to her as if time had slowed down. She 0:13:46.120 --> 0:13:48.320 would feel like time was passing, just as it would 0:13:48.360 --> 0:13:51.800 if she were standing perfectly still on Earth. A second 0:13:51.880 --> 0:13:54.280 would feel like a second to her. And in fact, 0:13:54.280 --> 0:13:57.000 if Alice were wearing a watch with a second hand, 0:13:57.679 --> 0:14:00.840 it would seem to be clicking one second at a time, 0:14:01.080 --> 0:14:04.720 just perfectly. Now, if Bob could somehow observe that watch 0:14:05.000 --> 0:14:07.320 while Alice is traveling at near the speed of light, 0:14:07.920 --> 0:14:12.120 Bob would see that the second hand is moving really slowly. 0:14:12.600 --> 0:14:15.800 It would be taking way longer than a second for 0:14:15.880 --> 0:14:20.120 it to take each tick. In fact, the faster you go, 0:14:20.360 --> 0:14:22.160 the slower it gets. And if you got to the 0:14:22.200 --> 0:14:24.880 point where you could travel at the speed of light, 0:14:25.560 --> 0:14:28.920 it would stop like the second hand wouldn't move anymore. 0:14:29.000 --> 0:14:31.600 For Bob, he wouldn't see the second If somehow Alice 0:14:31.600 --> 0:14:34.000 could move faster than the speed of light, which is 0:14:34.520 --> 0:14:37.360 as Einstein would put it impossible, it would look as 0:14:37.400 --> 0:14:39.840 though the second hand was going backwards. She would be 0:14:39.880 --> 0:14:43.560 traveling back in time. Now that's physically impossible. So I 0:14:43.600 --> 0:14:45.000 just thought I would throw head in there as an 0:14:45.000 --> 0:14:47.880 interesting you know, side note. But again to Alice, it 0:14:47.880 --> 0:14:50.800 would seem like time was passing as normal. And likewise, 0:14:51.120 --> 0:14:53.520 let's say Bob's wearing a watch. He has a second hand. 0:14:53.640 --> 0:14:56.880 To Bob, time is passing just as normal. A second 0:14:56.920 --> 0:14:59.640 takes a second, he can watch the little second hand 0:14:59.680 --> 0:15:02.800 click on buy on this on his watch. Now, let's 0:15:02.800 --> 0:15:05.640 say that Alice is able to see Bob's watch. While 0:15:05.720 --> 0:15:09.040 Alice is traveling at near light speed, it would look 0:15:09.040 --> 0:15:11.440 to her as if the second hand was going way 0:15:11.520 --> 0:15:15.040 too fast, like it was just spinning around the watch face. 0:15:15.440 --> 0:15:18.480 And again, Bob and Alice would each feel the passage 0:15:18.480 --> 0:15:21.240 of time as if it were just normal. It's only 0:15:21.480 --> 0:15:23.920 when they compare it to a point of reference, when 0:15:23.920 --> 0:15:28.200 they are relative to something else, that they see that 0:15:28.320 --> 0:15:32.280 there is any type of difference. Now, for most of 0:15:32.280 --> 0:15:35.760 our experiences on Earth, we don't notice this effect, and 0:15:35.800 --> 0:15:39.280 that's partly because we're usually traveling at a similar velocity 0:15:39.360 --> 0:15:42.400 relative to one another. We're all on this planet. Most 0:15:42.440 --> 0:15:45.440 of us aren't going super duper fast. However, there are 0:15:45.560 --> 0:15:49.560 cases where we can measure a difference. It wouldn't be 0:15:49.600 --> 0:15:53.640 observable like to our normal senses, but with very sensitive 0:15:54.680 --> 0:15:57.720 you know, metrics, we could see that there was a 0:15:57.760 --> 0:16:01.000 difference there. It's settled because we are not able to 0:16:01.040 --> 0:16:03.920 go anywhere close to the speed of light, at least 0:16:03.920 --> 0:16:07.200 not yet. So for example, we have the case of 0:16:07.240 --> 0:16:11.080 Mark and Scott Kelly. These are twin brothers who are 0:16:11.080 --> 0:16:14.880 both astronauts. Now, both of the Kelly's have spent time 0:16:14.960 --> 0:16:19.720 in orbit. Mark Kelly was born first, he's the older 0:16:19.760 --> 0:16:23.040 of the two twins, and he's logged fifty four days 0:16:23.040 --> 0:16:27.760 in space. Pretty respectable, right, I mean extremely respectable, Mr Kelly. 0:16:27.800 --> 0:16:32.560 I don't mean to, you know, dismiss that incredible achievement. 0:16:32.920 --> 0:16:37.080 But Scott Kelly has spent five hundred twenty days in orbit, 0:16:37.120 --> 0:16:40.760 almost ten times as much time in orbit, and a 0:16:40.800 --> 0:16:44.160 lot of that was aboard the International Space Station, which 0:16:44.240 --> 0:16:46.520 orbits the Earth at the speed of around twenty eight 0:16:46.520 --> 0:16:50.480 thousand kilometers per hour or seventeen thousand, five hundred miles 0:16:50.520 --> 0:16:54.120 per hour. So for a significant amount of time, Scott 0:16:54.160 --> 0:16:58.320 was traveling much faster relative to his brother Mark, who 0:16:58.360 --> 0:17:01.960 was back here on Earth. And since traveling faster means 0:17:02.000 --> 0:17:05.720 that time passes more slowly relative to an outside observer, 0:17:06.440 --> 0:17:09.920 it means that the gap between Mark and Scott actually 0:17:09.960 --> 0:17:14.880 got bigger. Mark aged faster here on Earth than Scott 0:17:14.960 --> 0:17:18.159 did out in space because of that speed of travel. 0:17:18.520 --> 0:17:20.959 Mark once said that he used to be six minutes 0:17:21.040 --> 0:17:23.760 older than his brother, but now, thanks to all that 0:17:23.880 --> 0:17:27.040 space travel that Scott did at high speeds, Mark is 0:17:27.240 --> 0:17:32.640 six minutes five milliseconds older. And that's a funny thing 0:17:32.680 --> 0:17:35.680 to say. Uh And sure you could argue, well, that's 0:17:35.680 --> 0:17:38.520 not really significant to our normal frame of reference. I mean, 0:17:38.560 --> 0:17:41.680 what's five milliseconds, But it does show that we actually 0:17:41.720 --> 0:17:44.119 have to keep this in mind when it comes to 0:17:44.240 --> 0:17:48.760 space travel. It does matter. Now when we come back, 0:17:49.600 --> 0:17:52.720 we're gonna tackle a little bit more of a relativity. 0:17:52.920 --> 0:18:05.200 But first let's take a relatively quick break. Okay, we're back, 0:18:05.240 --> 0:18:08.199 and we are not done with relativity yet. The speed 0:18:08.200 --> 0:18:12.000 and time thing is all part of special relativity. But 0:18:12.160 --> 0:18:16.240 Einstein was a real you know Einstein, and he also 0:18:16.320 --> 0:18:21.399 published his theory on general relativity. This includes an explanation 0:18:21.440 --> 0:18:24.320 that if you were to have two clocks and one 0:18:24.359 --> 0:18:27.679 of them is closer to a gravitational mass than the 0:18:27.720 --> 0:18:29.840 other one, the other one is much further out from 0:18:29.880 --> 0:18:33.760 that gravitational mass. The one that's closer to the gravitational 0:18:33.760 --> 0:18:37.680 mass will take more slowly than the one that's further out. 0:18:38.520 --> 0:18:41.440 This is separate from the whole you know, speed thing. 0:18:41.560 --> 0:18:45.040 So in other words, gravity also affects the rate at 0:18:45.080 --> 0:18:48.720 which time passes. It passes more slowly when you're closer 0:18:48.760 --> 0:18:53.720 to a big center of gravity. And this becomes really 0:18:53.760 --> 0:18:57.119 important for navigation just here on Earth, not even just 0:18:57.240 --> 0:19:01.200 space navigation, but navigation here. And you might wonder why 0:19:01.240 --> 0:19:04.439 that is. Well, a lot of us depend upon GPS 0:19:04.520 --> 0:19:07.600 apps or devices, right like we pull that up whenever 0:19:07.640 --> 0:19:11.720 we're going someplace new, and these devices they work by 0:19:11.720 --> 0:19:15.800 relying on signals that are coming from GPS satellites. It 0:19:15.840 --> 0:19:17.920 gets a few of these different signals and then it's 0:19:17.960 --> 0:19:22.000 able to pinpoint the location where on the surface of 0:19:22.000 --> 0:19:25.280 the Earth we happen to be at that given time. Well, 0:19:25.320 --> 0:19:28.720 those satellites are really far away from us. They are 0:19:28.760 --> 0:19:32.199 beyond low Earth orbit, so they're beyond where the International 0:19:32.200 --> 0:19:36.040 Space Station is, for example. They're out in medium Earth 0:19:36.119 --> 0:19:40.480 orbit somewhere around twenty two KOs out from the Earth, 0:19:40.560 --> 0:19:46.560 or around twelve fifty miles. So these satellites are much 0:19:46.840 --> 0:19:50.800 further out from the Earth's gravitational mass than say your 0:19:50.880 --> 0:19:54.040 watch or come on, we'll be real here your smartphone. 0:19:54.400 --> 0:19:58.359 So because of that, the clocks on the GPS satellites 0:19:58.440 --> 0:20:04.840 tick slightly fat stir. Then the clocks here on Earth tick. Remember, 0:20:04.880 --> 0:20:08.560 the closer you are to a gravitational mass, the slower 0:20:08.600 --> 0:20:13.439 time will pass for that particular frame of reference compared 0:20:13.480 --> 0:20:15.280 to a different frame of reference. I always have to 0:20:15.320 --> 0:20:20.280 throw that part in because again, in the moment it passes, 0:20:20.359 --> 0:20:22.879 the way time passes, like the way our experience of 0:20:22.920 --> 0:20:26.400 time is remains the same, not to our own frame 0:20:26.440 --> 0:20:30.439 of reference. Now, the GPS satellites are also traveling really 0:20:30.640 --> 0:20:33.679 fast relative to us, so that actually means that we 0:20:33.680 --> 0:20:36.240 have to take a bit off the top right, because 0:20:36.640 --> 0:20:40.800 we know that the faster you travel, the slower time 0:20:41.640 --> 0:20:45.160 uh affects you relative to someone who's not traveling at 0:20:45.200 --> 0:20:48.960 that speed. So the effects of general relativity mean that 0:20:49.000 --> 0:20:51.960 a clock on a GPS satellite has on average around 0:20:51.960 --> 0:20:55.040 forty five micro seconds more than an Earth clock at 0:20:55.080 --> 0:20:58.520 the end of a day, a full day. But again, 0:20:58.600 --> 0:21:02.520 because these satellites are link faster relative to us, the 0:21:02.600 --> 0:21:07.000 clocks also have a negative seven micro seconds two factor, 0:21:07.040 --> 0:21:10.000 and compared to our clocks, due to special relativity, so 0:21:10.040 --> 0:21:12.520 we have to combine those two together forty five and 0:21:12.600 --> 0:21:16.600 negative seven. That gives us thirty eight micro seconds that 0:21:16.720 --> 0:21:22.119 are extra on the GPS clocks. So if if we 0:21:22.119 --> 0:21:25.160 were to stop it right at midnight for both clocks, 0:21:25.359 --> 0:21:28.080 you know here on Earth and at the GPS satellite, 0:21:28.280 --> 0:21:31.840 we would see midnight on our clock and midnight plus 0:21:31.880 --> 0:21:35.679 thirty eight million micro seconds, not milliseconds micro seconds on 0:21:35.720 --> 0:21:39.520 the GPS side. Now, because our navigation depends upon taking 0:21:39.560 --> 0:21:42.960 signals from satellites and essentially measuring how long it took 0:21:43.520 --> 0:21:46.040 for that signal to go from the satellite to us, 0:21:46.400 --> 0:21:50.040 in order for us to calculate where we are on Earth, 0:21:50.680 --> 0:21:53.879 we actually have to account for that difference between our 0:21:53.880 --> 0:21:58.560 clocks and the satellite satellites clocks, or else we start 0:21:58.600 --> 0:22:01.639 to get some drift, and that means that over time, 0:22:01.960 --> 0:22:04.600 and and we're actually talking about years here, but it 0:22:04.640 --> 0:22:08.800 does happen, our navigation systems would become less accurate, which 0:22:08.800 --> 0:22:11.800 would eventually get to a point where our GPS device 0:22:12.280 --> 0:22:15.040 wouldn't even really show us where we are because it 0:22:15.080 --> 0:22:20.400 would be miscalculating based upon the the differences in the 0:22:20.520 --> 0:22:24.080 clocks on the GPS satellites versus the clock on our 0:22:24.119 --> 0:22:27.560 phone or that our phone is connected to, and instead 0:22:27.560 --> 0:22:30.720 it would show you where it thinks you are, but 0:22:30.880 --> 0:22:33.640 there would be a growing gap between where it thinks 0:22:33.680 --> 0:22:36.160 you are and where you really are. Based upon this 0:22:36.200 --> 0:22:39.080 gap in time. It would take like seven years for 0:22:39.160 --> 0:22:41.520 that to get to a point where we might even 0:22:41.560 --> 0:22:45.240 notice it, and we do correct for it. So essentially 0:22:45.280 --> 0:22:48.080 what happens is we shave thirty eight micro seconds off 0:22:48.200 --> 0:22:53.239 the clocks every midnight that the that the clock's hit. 0:22:53.320 --> 0:22:56.640 So when the clocks hit midnight on the GPS satellites, 0:22:56.680 --> 0:22:59.600 they kind of hold for thirty eight microseconds, which puts 0:22:59.600 --> 0:23:02.000 them I can sync with the clocks here on Earth. 0:23:02.400 --> 0:23:03.920 And then we have to do it every single day 0:23:04.000 --> 0:23:08.080 because every single day we get the effects of relativity. 0:23:08.640 --> 0:23:11.400 All right, well, that's something we have to take into 0:23:11.480 --> 0:23:16.919 account with navigation, Like these are things that we don't again, 0:23:16.960 --> 0:23:20.320 we don't necessarily have to think about here on Earth. Typically, 0:23:21.160 --> 0:23:24.399 most of us don't come into situations where special and 0:23:24.480 --> 0:23:28.800 general relativity have a noticeable impact on our day to 0:23:28.880 --> 0:23:34.119 day experience. UM. One really important element in space navigation 0:23:34.720 --> 0:23:37.960 is something called the deep Space Network, which is not 0:23:38.040 --> 0:23:41.280 a really cool science fiction channel, uh, no, it's it's 0:23:41.320 --> 0:23:44.920 actually a bunch of antennas, and it's it's more than that. 0:23:45.040 --> 0:23:47.959 But that's a big part of it. If we go 0:23:48.040 --> 0:23:51.120 back to the nineteen fifties, we had the space race 0:23:51.280 --> 0:23:54.800 ramping up. In nineteen fifty seven, the then Soviet Union 0:23:54.880 --> 0:23:58.840 launched spot Nick into orbit. The US was already working 0:23:58.840 --> 0:24:02.200 on its own satellite, and of course there were reasons 0:24:02.240 --> 0:24:05.800 for this beyond the scientific push. Scientific push was a 0:24:05.840 --> 0:24:08.479 big part of it, but there were other political reasons. 0:24:08.520 --> 0:24:11.200 For one thing, Demonstrating that you could put a payload 0:24:11.200 --> 0:24:15.359 into space also sent the message of hey, comrade, we 0:24:15.400 --> 0:24:17.800 can build rockets big enough to reach you, even though 0:24:17.800 --> 0:24:19.679 we're on the other side of the world, and you know, 0:24:19.800 --> 0:24:24.280 nuclear weapons are a thing, so you know, this wasn't 0:24:24.640 --> 0:24:29.840 just you know, a science thing. But that's another tangent 0:24:29.960 --> 0:24:32.320 that I won't go down any further. But on the 0:24:32.440 --> 0:24:35.280 U s side, one of the things that the Jet 0:24:35.280 --> 0:24:39.679 Propulsion Laboratory or JPL undertook was a job from the 0:24:39.760 --> 0:24:43.400 United States Army, which effectively you know, ran the jp 0:24:43.640 --> 0:24:47.639 L to establish radio tracking stations in certain parts of 0:24:47.640 --> 0:24:53.160 the world, including places like Singapore, Nigeria, and California. So upon, 0:24:53.280 --> 0:24:57.120 launching the first successful US satellite, which was called Explorer one. 0:24:57.960 --> 0:25:01.240 These ground stations would receive data from the satellite to 0:25:01.240 --> 0:25:05.280 be able to track it as it passed over overhead. 0:25:05.640 --> 0:25:08.760 This was essentially telemetry data, and you might wonder what 0:25:08.800 --> 0:25:12.399 does that mean. Well, telemetry is essentially the process of 0:25:12.520 --> 0:25:15.680 using some sort of device to measure something. It could 0:25:15.680 --> 0:25:18.960 be temperature, it could be pressure, it could be speed 0:25:19.160 --> 0:25:23.680 or velocity, and then it transmits that information to a 0:25:23.760 --> 0:25:27.439 distant receiver. Now, in this case, the telemetry was mostly 0:25:27.480 --> 0:25:31.680 about the Explorer one's orientation and velocity as it went 0:25:31.720 --> 0:25:35.879 through its orbit. Engineers at mission control could take that 0:25:36.040 --> 0:25:40.560 data and plot out the Explorer one's orbital path. In October, 0:25:41.800 --> 0:25:45.320 the US government established NASA, and this was really to 0:25:45.359 --> 0:25:49.840 consolidate the space efforts from various independent groups, mostly in 0:25:49.920 --> 0:25:52.960 the military, like the Army, Navy, and Air Force all 0:25:53.040 --> 0:25:58.800 had independent space exploration UH initiatives, so this was to 0:25:58.880 --> 0:26:03.120 kind of bring them all under one civilian umbrella and 0:26:03.240 --> 0:26:07.679 combine all those resources to be more effective. So this 0:26:07.760 --> 0:26:12.720 included the Jet Propulsion Laboratory that had previously been run 0:26:12.800 --> 0:26:16.040 by the U. S Army that became part of NASA. 0:26:16.080 --> 0:26:19.159 In December of nineteen and NASA would assign to the 0:26:19.240 --> 0:26:22.879 jp L the responsibility of planning out planetary and lunar 0:26:22.960 --> 0:26:27.800 exploration missions that would use unscrewed spacecraft, that is, spacecraft 0:26:27.840 --> 0:26:30.760 that did not have human beings abort robotic spacecraft if 0:26:30.760 --> 0:26:34.119 you prefer. Now. That would necessitate a network system of 0:26:34.200 --> 0:26:37.919 receivers here on Earth to be able to receive communications 0:26:38.000 --> 0:26:41.119 with and then to send communications too, as well as 0:26:41.160 --> 0:26:45.000 to just keep track of these robotic spacecraft as they 0:26:45.040 --> 0:26:48.560 traveled away from the Earth. You can't just have one 0:26:48.840 --> 0:26:52.960 really big antenna in Houston, because you know, the Earth 0:26:53.080 --> 0:26:57.119 rotates and sometimes Houston would be pointing the wrong way. 0:26:57.320 --> 0:27:02.120 Get together, Houston. So yeah, to establish that these antenna 0:27:02.280 --> 0:27:04.880 around the Earth need to be pointing outward in such 0:27:04.920 --> 0:27:09.800 a way that you have maintained contact with distant spacecraft. Moreover, 0:27:10.240 --> 0:27:13.919 as the spacecraft move further from the Earth, the signal 0:27:13.960 --> 0:27:17.120 strength will decrease. In fact, you know, here on Earth 0:27:17.160 --> 0:27:20.880 we describe radio frequencies as obeying the inverse square law, 0:27:20.960 --> 0:27:23.800 which means that the power of a signal is inversely 0:27:23.840 --> 0:27:30.600 proportional to the distance from a source. Hey, it's Jonathan 0:27:30.640 --> 0:27:34.479 from one day further out from when this episode originally published. Okay, 0:27:34.520 --> 0:27:37.119 so the first time I tried to explain this, I 0:27:37.640 --> 0:27:41.000 just playing god it all wrong. Uh, we published the episode, 0:27:41.240 --> 0:27:43.879 they had an error in it, and this was because 0:27:43.880 --> 0:27:48.080 of a fundamental misunderstanding on my part. But fortunately Charlie 0:27:48.160 --> 0:27:50.480 Tango Bravo on Twitter set me straight and I'm gonna 0:27:50.480 --> 0:27:54.000 try harder to get it right this time. So the 0:27:54.040 --> 0:27:56.919 inverse square law will first imagine that you have a 0:27:56.960 --> 0:28:00.520 source of electro magnetic radiation. And this can be anything 0:28:00.640 --> 0:28:06.000 from you know, a radio antenna to a microwave source 0:28:06.040 --> 0:28:09.560 to light. In fact, let's talk about light because that's 0:28:09.560 --> 0:28:11.600 pretty easy for us to wrap our heads around it 0:28:11.600 --> 0:28:14.440 because we can directly observe it. Right, We've all seen 0:28:14.560 --> 0:28:16.720 that as you move away from a source of light, 0:28:17.200 --> 0:28:20.719 then you get less light to work with, Right, that's intuitive. 0:28:21.080 --> 0:28:24.520 So if you're walking around I don't know, a spooky 0:28:24.600 --> 0:28:28.000 attic and it's lit by a single light bulb hanging 0:28:28.040 --> 0:28:31.600 down from a chain, well you know that as you 0:28:31.640 --> 0:28:33.840 get towards the corners, a ghost is gonna get you. 0:28:34.520 --> 0:28:37.720 I'm kidding. Ghosts don't exist, but you do know that 0:28:37.760 --> 0:28:39.640 as you move further away from the light, bulb, it 0:28:39.680 --> 0:28:44.320 gets darker, Right, That just something we've experienced. Well, we 0:28:44.320 --> 0:28:48.280 can actually describe this phenomena with the inverse square law 0:28:48.320 --> 0:28:52.760 of propagation. We can think of radiation moving out from 0:28:52.880 --> 0:28:57.560 a source as similar to that of an expanding sphere, 0:28:58.040 --> 0:29:01.000 like it's going out in all directions and growing as 0:29:01.040 --> 0:29:03.560 it moves outward. Right, the sphere gets bigger and bigger. 0:29:03.960 --> 0:29:09.280 The center is still stationary in this frame of reference. 0:29:09.720 --> 0:29:12.200 So the further we get out from the center of 0:29:12.240 --> 0:29:17.000 the sphere, the more surface area that electromagnetic radiation is covering. Right, 0:29:17.080 --> 0:29:21.280 the the outside of the sphere is bigger. That means 0:29:21.320 --> 0:29:23.360 that the signal strength is growing weaker. You have the 0:29:23.400 --> 0:29:26.880 same amount of signal to go around, but you're covering 0:29:26.960 --> 0:29:28.760 a larger area, so you can think of it as 0:29:28.800 --> 0:29:32.480 spreading across more space. And we can describe the relationship 0:29:32.480 --> 0:29:37.440 between signal intensity and distance as intensity equals one divided 0:29:37.480 --> 0:29:41.800 by r, that being the distance squared. So if you 0:29:42.000 --> 0:29:45.080 double the distance between you and a source, if you 0:29:45.480 --> 0:29:48.520 make are twice as big, the intensity you observe will 0:29:48.600 --> 0:29:51.400 drop by a factor of four. So if you went 0:29:51.400 --> 0:29:54.640 from one to two, then the intensity would go down 0:29:54.680 --> 0:29:56.880 to a quarter of what it used to be, you've 0:29:56.880 --> 0:29:59.200 reduced it by a factor of four. If you were 0:29:59.240 --> 0:30:03.840 to triple the distance between you and the source, then 0:30:04.160 --> 0:30:07.880 the intensity would reduce by a factor of nine. Three 0:30:07.920 --> 0:30:11.400 squared is nine, and so on and so forth. So 0:30:12.120 --> 0:30:15.840 I described in the previous version that signal does decrease 0:30:16.040 --> 0:30:19.040 as distance increases. That part was right, but the relationship 0:30:19.080 --> 0:30:22.120 I got totally wrong. The important thing to remember is 0:30:22.160 --> 0:30:25.080 that the signal strength drops off as we get further 0:30:25.160 --> 0:30:27.760 away from the source. So for spacecraft that are traveling 0:30:27.800 --> 0:30:30.640 further from Earth, that's a big factor we have to 0:30:30.640 --> 0:30:35.160 take into consideration. All right, let's get back to the 0:30:35.160 --> 0:30:39.760 original episode, and again, thank you to Charlie Tango Bravo 0:30:39.920 --> 0:30:42.360 for setting me on the right path. I appreciate it. 0:30:45.800 --> 0:30:47.560 And we also have to remember that there's a lot 0:30:47.560 --> 0:30:50.520 of stuff that generates radio signals. I mean, there's a 0:30:50.520 --> 0:30:53.320 ton of stuff here on Earth that we create, like 0:30:53.640 --> 0:30:57.360 TV and radio and cell phones and that kind of stuff. 0:30:57.560 --> 0:31:00.360 Those generate radio signals. But they're also a lot of 0:31:00.400 --> 0:31:04.360 things in space that generate radio signals, like pulsars and 0:31:04.560 --> 0:31:08.320 nebula and quasars. So in other words, there's a lot 0:31:08.360 --> 0:31:12.000 of potential noise to deal with when we're looking for 0:31:12.080 --> 0:31:16.200 a radio signal. So again, finding that that signal amid 0:31:16.280 --> 0:31:19.560 all the noise is a big challenge. It doesn't it's 0:31:19.560 --> 0:31:23.360 not just important that our antenna is sensitive. We have 0:31:23.440 --> 0:31:26.080 to have it really directional so that we can make 0:31:26.160 --> 0:31:29.520 certain that we're pointing at the thing we want to 0:31:29.520 --> 0:31:35.560 to listen to. Otherwise we might mistake some errant Earth 0:31:35.680 --> 0:31:39.840 generated signal as being our spacecraft and then we're on 0:31:39.880 --> 0:31:43.920 the wrong track. So to meet these challenges, NASA, through 0:31:43.960 --> 0:31:47.680 the JPL, established the Deep Space Network or d s N. 0:31:48.320 --> 0:31:51.760 The DSN has three facilities that are approximately a hundred 0:31:51.800 --> 0:31:56.200 twenty degrees apart in longitude, so that means they're roughly 0:31:56.360 --> 0:32:01.680 equidistant from each other Longitudinally, you multiply one twenty by three, 0:32:01.920 --> 0:32:06.080 you get three sixty. That's a circle, right. So one 0:32:06.120 --> 0:32:09.400 of the three is in Goldstone, California. That's actually in 0:32:09.440 --> 0:32:13.200 the desert. It's northeast of Los Angeles, it's south of 0:32:13.320 --> 0:32:16.360 Death Valley, and it's pretty far away from stuff that 0:32:16.400 --> 0:32:21.200 generates radio waves. The second is in Madrid, Spain, so 0:32:21.200 --> 0:32:24.600 that's almost smack dab in the middle of Spain. The 0:32:24.720 --> 0:32:28.920 third is in Canberra, Australia, which is on the coast 0:32:28.920 --> 0:32:33.560 in the southeast of Australia, and it's probably covered with 0:32:33.720 --> 0:32:39.040 venomous animals. I mean it's Australia, so it's a safe bet. 0:32:39.600 --> 0:32:42.040 So again, because these sites are a hundred twenty degrees 0:32:42.080 --> 0:32:45.280 apart from each other, we get that three hundred sixty 0:32:45.400 --> 0:32:49.440 degree view if you will, of the space around Earth. 0:32:50.000 --> 0:32:52.560 And what this means is that at any given time, 0:32:52.760 --> 0:32:56.160 at least one of the three DS insights has the 0:32:56.160 --> 0:33:00.200 ability to establish a line of sight communication channel with 0:33:00.440 --> 0:33:05.280 a distant spacecraft. And as the world rotates and one 0:33:05.480 --> 0:33:09.720 of these sites begins to lose contact, the next one 0:33:10.120 --> 0:33:13.680 will pick it right up, so communications can remain online. 0:33:13.720 --> 0:33:16.960 You don't have an interruption. This is a big thing. 0:33:17.040 --> 0:33:21.280 Like you might remember when I was talking about space stations. 0:33:21.400 --> 0:33:26.160 When the most recent as of this recording, anyway, when 0:33:26.160 --> 0:33:29.760 the most recent module joined the International Space Station, it 0:33:29.880 --> 0:33:35.200 was the Naka from the from Russia. When it docked, 0:33:35.560 --> 0:33:39.600 its thrusters misfired. They weren't supposed to fire, but they did, 0:33:40.080 --> 0:33:44.320 and it caused the space station to rotate and move 0:33:44.360 --> 0:33:48.400 into the wrong orientation relative to the Earth. Well, when 0:33:48.440 --> 0:33:52.239 that happened. The space station was not in range of 0:33:52.520 --> 0:33:56.160 Russia's mission control because that was on the wrong side 0:33:56.200 --> 0:33:58.040 of the Earth at the time, and that was a 0:33:58.040 --> 0:34:01.880 problem because Russia was the only entity that had the 0:34:01.920 --> 0:34:06.240 ability to control the thrusters on the Knocka. So that's 0:34:06.240 --> 0:34:10.200 an example of why it's important to have established these 0:34:10.239 --> 0:34:15.239 points where we can have uninterrupted contact. All right, we've 0:34:15.280 --> 0:34:18.520 got more to say about navigation, but before I get 0:34:18.560 --> 0:34:29.839 totally lost, let's take another quick break. So at these 0:34:29.880 --> 0:34:35.359 different sites at Goldstone, California, and Madrid, Spain, Canberra, Australia, 0:34:35.960 --> 0:34:41.040 they have a series of radio telescopes, including one really 0:34:41.080 --> 0:34:43.799 big one at each of these sites, and the deep 0:34:43.840 --> 0:34:47.960 space radio antenna can be extremely impressive. So the Goldstone 0:34:48.480 --> 0:34:52.319 Mars dish, that's the biggest one at gold Stone, California. 0:34:52.760 --> 0:34:55.399 That one was built in nineteen but it was later 0:34:55.560 --> 0:35:00.800 upgraded in night so today it measures seventy eaters across, 0:35:00.920 --> 0:35:04.880 that's about two thirty feet. Now, this dish has a 0:35:04.920 --> 0:35:10.239 surface area of around an acre or square feet or 0:35:10.400 --> 0:35:14.400 three thousand, eight hundred fifty square meters. It weighs nearly 0:35:14.520 --> 0:35:20.080 three thousand tons. It's mounted on massive machinery that can 0:35:20.120 --> 0:35:23.160 tilt and turn the dish so that it can be 0:35:23.239 --> 0:35:27.960 aimed precisely where a spacecraft is overhead and get you know, 0:35:28.200 --> 0:35:32.600 that laser like focus with a communications channel with a 0:35:32.600 --> 0:35:36.680 spacecraft that could be millions or billions of miles from 0:35:36.719 --> 0:35:40.200 the Earth. And the purpose of those big big dishes, 0:35:41.120 --> 0:35:44.080 I mean, it's all about collecting the very weak radio 0:35:44.280 --> 0:35:47.560 energy that's being sent back from the spacecraft. You know, 0:35:47.560 --> 0:35:51.839 because again that distances is intense, like the signals are 0:35:52.080 --> 0:35:55.160 very very weak by the time they get back to Earth, 0:35:55.280 --> 0:35:59.520 especially for super distant spacecraft. So this big dish is 0:35:59.520 --> 0:36:03.400 able to like that energy and then direct it toward 0:36:03.440 --> 0:36:07.440 the antenna itself, so you can think of it this parabola. 0:36:07.560 --> 0:36:11.960 It's all focusing that radio energy to a specific point, 0:36:12.000 --> 0:36:16.160 that point being the end of the actual radio antenna. 0:36:16.320 --> 0:36:18.919 Otherwise the signal would be so weak that it would 0:36:18.920 --> 0:36:21.799 be difficult, if not impossible, to detect that signal through 0:36:21.840 --> 0:36:25.360 all the noise, and engineers have to position and antenna 0:36:25.480 --> 0:36:29.319 precisely to beam radio instructions back to the distant spacecraft. 0:36:29.840 --> 0:36:32.840 If you're off even by a little bit, the message 0:36:32.880 --> 0:36:34.960 is not going to end up going to where you 0:36:35.000 --> 0:36:37.719 need it to. Go, and the further out the spacecraft 0:36:37.800 --> 0:36:40.399 is from Earth, the more critical it becomes to get 0:36:40.400 --> 0:36:44.319 that just right. So all of that is to set 0:36:44.400 --> 0:36:48.320 up the actual talk about navigation itself. We had to 0:36:48.360 --> 0:36:52.400 set all those parameters to talk about the process. Without 0:36:52.440 --> 0:36:54.840 the system like the Deep Space Network in place to 0:36:54.880 --> 0:36:58.560 communicate with spacecraft navigation would be impossible. We would not 0:36:58.600 --> 0:37:03.000 be able to build a spacecraft capable of detecting its 0:37:03.040 --> 0:37:07.239 own orientation and velocity and to make changes on the fly. 0:37:07.760 --> 0:37:10.520 It's not like Star Trek or Star Wars, where you 0:37:10.560 --> 0:37:12.760 just tell an on ship computer to plot a course 0:37:12.800 --> 0:37:18.799 for Javin or whatever. NASA describes space navigation as being 0:37:19.080 --> 0:37:23.880 the domain of three large departments within NASA. There's mission design, 0:37:24.520 --> 0:37:29.600 there's orbit determination, and there's flight path control. These three 0:37:29.640 --> 0:37:33.040 things all inter relate to one another. So first we 0:37:33.080 --> 0:37:36.320 have mission design. Now, this is the part of navigation 0:37:36.320 --> 0:37:39.719 in which mission control has to determine what the intended 0:37:40.040 --> 0:37:45.359 trajectory is for the spacecraft, where is it supposed to go. Now, 0:37:45.360 --> 0:37:47.959 this alone is tricky for all the reasons that I've 0:37:47.960 --> 0:37:50.759 talked about earlier in this episode. You've got to take 0:37:50.920 --> 0:37:54.920 all those different elements into consideration, like relativity. You know, 0:37:55.080 --> 0:37:57.560 what is it that you're hoping to do? What what 0:37:57.680 --> 0:38:00.960 is the purpose of the spacecraft? What are the things 0:38:01.000 --> 0:38:03.720 that are going to affect the spacecraft as it travels 0:38:03.760 --> 0:38:06.040 from Earth to get to where it's supposed to go. 0:38:06.520 --> 0:38:09.719 How do you account for those things? And how do 0:38:09.760 --> 0:38:14.239 you either incorporate stuff so that it, you know, it 0:38:14.320 --> 0:38:16.720 becomes part of your mission, or how do you find 0:38:16.760 --> 0:38:21.680 a way around an obstacle or challenge. Now, keep in mind, 0:38:22.480 --> 0:38:25.759 we learn new stuff the more we send spacecraft up, 0:38:26.040 --> 0:38:29.080 Like we learn more every single time, and some of 0:38:29.120 --> 0:38:32.760 that stuff is important and it affects calculations, like important 0:38:32.760 --> 0:38:35.680 for the sense of navigation, that is, it's always important. 0:38:36.600 --> 0:38:39.879 Someone has to take the things we've learned and then 0:38:39.960 --> 0:38:43.799 build that into software that we use to calculate complex 0:38:43.800 --> 0:38:47.440 equations in order to plot out navigation. So space navigation 0:38:47.840 --> 0:38:50.640 is something that has evolved over time, and as we 0:38:50.760 --> 0:38:54.759 learn more and incorporate what we've learned into the next 0:38:54.840 --> 0:38:59.440 generation of software, it's constantly in a state of change. 0:38:59.800 --> 0:39:02.719 So one thing that engineers have to factor in is 0:39:02.760 --> 0:39:06.160 the fact that a spacecraft is always orbiting. Something I 0:39:06.239 --> 0:39:08.760 kind of indicated this at the top of the show. 0:39:09.520 --> 0:39:11.440 You know, it could orbit the Earth. It could be 0:39:11.480 --> 0:39:14.160 in low Earth orbit and just stay there, but it's 0:39:14.200 --> 0:39:18.120 in orbit. Or you might want it to leave Earth 0:39:18.280 --> 0:39:21.960 orbit and enter into a solar orbit, so now it's 0:39:22.040 --> 0:39:26.799 orbiting the Sun just like Earth or Mars, or you know, 0:39:26.840 --> 0:39:28.960 any of the other planets are. Maybe you want to 0:39:29.080 --> 0:39:33.319 enter into a different planets orbit. Maybe you want it 0:39:33.360 --> 0:39:36.080 to leave the Solar System entirely, in which case it's 0:39:36.120 --> 0:39:39.080 in a galactic orbit. It's orbiting the center of the 0:39:39.120 --> 0:39:42.319 Milky Way, just like our Solar system is. It does 0:39:42.400 --> 0:39:44.800 require an awful lot of velocity in order to escape 0:39:44.800 --> 0:39:47.520 the Solar System. By the way, but we have done it, 0:39:47.920 --> 0:39:50.960 not with you know, humans obviously, but with spacecraft we've 0:39:51.000 --> 0:39:56.160 sent out anyway. Orbits are a huge part of navigation calculations. 0:39:56.280 --> 0:40:00.000 And again you're talking about an origin and a destination, 0:40:00.080 --> 0:40:03.560 and that are from an outside reference both in motion, 0:40:04.120 --> 0:40:07.080 and we have to take into account the effects of 0:40:07.080 --> 0:40:10.000 stuff like relativity with spacecraft. That's going to affect things 0:40:10.080 --> 0:40:13.759 like the clocks on board the spacecraft. That means we 0:40:13.760 --> 0:40:16.719 have to account for those changes due to relativity or 0:40:16.760 --> 0:40:20.080 else we risk losing track of the spacecraft. We might 0:40:20.200 --> 0:40:24.160 point an antenna at where a spacecraft either used to 0:40:24.200 --> 0:40:28.120 be or might be in the future, but isn't right now, 0:40:28.320 --> 0:40:32.280 just because we have these deviations from between our earthbound 0:40:32.280 --> 0:40:35.319 clocks and the ones that are aboard the spacecraft. So 0:40:35.719 --> 0:40:39.440 the software has to plot a trajectory that has to 0:40:39.480 --> 0:40:42.600 take all these different things into consideration, and as you 0:40:42.600 --> 0:40:47.040 can imagine, this means those calculations get pretty darn complicated, 0:40:47.080 --> 0:40:51.000 particularly when you're looking at something you know, really ambitious, 0:40:51.480 --> 0:40:53.959 which sounds a little weird to say, because I still 0:40:54.000 --> 0:40:56.680 think just getting something into low Earth orbit is being 0:40:56.760 --> 0:41:00.600 really ambitious. But you know, there's there is a scale, 0:41:00.680 --> 0:41:03.640 I guess, and as I'm sure we're all aware, software 0:41:03.680 --> 0:41:06.440 does not always come out perfect, right. You've probably used 0:41:06.480 --> 0:41:09.719 software where you've encountered a bug or a glitch, Like 0:41:10.160 --> 0:41:13.360 maybe you're playing a video game and the textures failed 0:41:13.360 --> 0:41:17.640 to load and everything looks weird. Well, that's irritating when 0:41:17.640 --> 0:41:20.279 it's a video game, but when you're talking about like 0:41:20.520 --> 0:41:25.279 interplanetary navigation, a bug or glitch can become an enormous challenge. Now, 0:41:25.280 --> 0:41:27.600 it might not be a show stopper. You might be 0:41:27.640 --> 0:41:30.600 able to work around it, but it likely will require 0:41:30.640 --> 0:41:32.239 a lot of people to work out a solution on 0:41:32.280 --> 0:41:34.120 the fly in order to make a sure that a 0:41:34.160 --> 0:41:38.000 spacecraft's route is in fact the right one to do 0:41:38.080 --> 0:41:41.359 whatever it is you want that spacecraft to do, all right. So, 0:41:42.640 --> 0:41:45.120 once all of that has been taken into account, engineers 0:41:45.160 --> 0:41:49.560 calculate the navigational route for a spacecraft. This planned route 0:41:49.880 --> 0:41:53.880 is the reference trajectory, so this is the route the 0:41:53.920 --> 0:41:59.200 spacecraft should be on. Also, there's a cesall relationship between 0:41:59.239 --> 0:42:02.560 the navigator for a mission and the software developers who 0:42:02.560 --> 0:42:05.840 are making the navigation software. So as navigators find bugs 0:42:05.960 --> 0:42:09.600 or they encounter new situations that necessitate new features in 0:42:09.640 --> 0:42:12.960 the software, they can relay that to the developers, and 0:42:13.000 --> 0:42:15.520 then they take the feedback and they produce new versions 0:42:15.520 --> 0:42:19.279 of the software. I imagine that gets increasingly challenging to do, 0:42:19.400 --> 0:42:22.799 especially to incorporate new features. Any developer can tell you 0:42:23.280 --> 0:42:26.600 that it can be a nightmare to put something new 0:42:26.680 --> 0:42:29.040 into code that you've just gotten to work, because the 0:42:29.360 --> 0:42:31.960 chances are you're going to break something that previously had 0:42:32.000 --> 0:42:35.359 been working. Okay, just imagine that for things that are 0:42:35.400 --> 0:42:38.799 traveling through space and you have to deal with relativity 0:42:38.840 --> 0:42:43.360 and stuff. Now, even when you do that correctly, which 0:42:43.440 --> 0:42:46.439 you know obviously requires a lot of work. It does 0:42:46.480 --> 0:42:48.920 not mean that a spacecraft is just going to magically 0:42:49.040 --> 0:42:53.879 stick to that reference trajectory. All sorts of things can 0:42:53.920 --> 0:42:57.879 cause the spacecraft to deviate from the planned route. In 0:42:57.920 --> 0:43:00.879 some cases, it might be on purpose us such as 0:43:01.280 --> 0:43:03.640 you know, you might have to do a maneuver to 0:43:03.719 --> 0:43:07.640 avoid a potential collision. Or it might be that your 0:43:07.680 --> 0:43:11.279 pathway is taking you close to a planet and you're 0:43:11.320 --> 0:43:15.680 planning on using a gravity assist two make the spacecraft 0:43:15.680 --> 0:43:19.560 continuance journey. But in other cases, something might pop up 0:43:19.840 --> 0:43:25.080 that wasn't anticipated, Like it happens very quickly. Maybe the 0:43:25.080 --> 0:43:29.080 spacecraft passes some large asteroids and the gravitational attraction between 0:43:29.120 --> 0:43:32.040 the spacecraft and the asteroids pulls the craft out of 0:43:32.080 --> 0:43:35.080 its trajectory a bit. Or maybe it turns out that 0:43:35.160 --> 0:43:37.400 the software had a bug in it or a blind 0:43:37.440 --> 0:43:40.480 spot that failed to account for something, and the spacecraft 0:43:40.560 --> 0:43:43.399 is veering off course a bit as a result. I mean, 0:43:43.480 --> 0:43:50.000 even solar pressure, that is pressure from light itself hitting 0:43:50.000 --> 0:43:53.959 the spacecraft can be enough to push the spacecraft off 0:43:54.040 --> 0:43:59.399 its reference trajectory. This is where orbit determination comes in. Now, 0:43:59.440 --> 0:44:03.080 as the name implies, this part of space navigation is 0:44:03.120 --> 0:44:07.640 just keeping track of a spacecraft's actual position. We know 0:44:07.920 --> 0:44:11.279 where we want the spacecraft to go, but this is 0:44:11.400 --> 0:44:16.200 about us figuring out where the spacecraft actually is. And 0:44:17.080 --> 0:44:20.960 that is another kittle of fish. NASA breaks down orbit 0:44:21.000 --> 0:44:27.120 determination into three sub processes or subgroups, So there's orbit reconstruction. 0:44:27.520 --> 0:44:31.200 This is asking the question where has this spacecraft been? 0:44:31.719 --> 0:44:35.200 This is all about determining the past route, the past 0:44:35.239 --> 0:44:40.360 locations for the spacecraft to understand its actual trajectory versus 0:44:40.440 --> 0:44:44.719 the reference trajectory. Then you've got orbit determination. This is 0:44:44.760 --> 0:44:47.759 like asking where the heck is the ding dang thing 0:44:47.880 --> 0:44:51.600 right now? Then you've got orbit prediction. This is like 0:44:51.640 --> 0:44:54.400 asking where the heck is this thing going to next? 0:44:55.080 --> 0:44:56.440 And and at this point I kind of wish I 0:44:56.480 --> 0:44:59.960 hadn't burned the mean Girls reference about gettin loser we're 0:45:00.000 --> 0:45:04.080 going shopping, But I did that one already. Anyway, A 0:45:04.120 --> 0:45:08.440 bit of consideration reveals that all three of these things 0:45:08.480 --> 0:45:13.680 are important. See, we're not controlling these spacecraft in real time. 0:45:13.920 --> 0:45:17.080 You know, you don't have someone sitting looking at a monitor. 0:45:17.239 --> 0:45:20.040 They get a first person view of a spacecraft's viewscreen. 0:45:20.360 --> 0:45:22.920 They've got a joystick and they're just making it fly 0:45:23.080 --> 0:45:25.840 all over the place. That's not how this works. And 0:45:25.960 --> 0:45:28.319 it does take time for a signal to pass from 0:45:28.400 --> 0:45:31.160 one point in space to another. The fastest that this 0:45:31.320 --> 0:45:34.200 can happen at is the speed of light, and you know, 0:45:34.480 --> 0:45:38.200 light is wicked fast. It's in fact the fastest stuff 0:45:38.320 --> 0:45:43.400 there is. But light can't traverse great distances in an instant. 0:45:43.760 --> 0:45:46.279 I mean it takes about eight minutes for light to 0:45:46.320 --> 0:45:49.560 go from the Sun to hit us here on Earth. 0:45:49.960 --> 0:45:53.560 So as as spacecraft gets further from the Earth, the 0:45:53.640 --> 0:45:58.120 information that we get back from those spacecraft becomes more dated. Right, 0:45:58.239 --> 0:46:01.439 it's more about where the space was at the time 0:46:01.480 --> 0:46:05.399 it transmitted, but minutes have passed between then and when 0:46:05.440 --> 0:46:08.319 we're able to actually look at the data. So as 0:46:08.400 --> 0:46:11.960 engineers get the latest telemetric data, they're actually looking at 0:46:12.239 --> 0:46:15.600 stuff that's several minutes old. So we're not observing the 0:46:15.680 --> 0:46:19.880 spacecraft directly. We're getting information back from the spacecraft, and 0:46:20.000 --> 0:46:22.640 then we have to draw conclusions about what's going on 0:46:23.320 --> 0:46:26.520 based upon the information we have. So if the data 0:46:26.600 --> 0:46:29.879 indicates that perhaps a ship is drifting away from its 0:46:29.960 --> 0:46:32.919 reference trajectory, we need to be able to look back 0:46:33.360 --> 0:46:36.239 and see what the data has said about that. When 0:46:36.320 --> 0:46:39.759 did that deviation begin? How long has it been going on? 0:46:40.280 --> 0:46:43.239 Where is the spacecraft now? Based on the information we have, 0:46:43.760 --> 0:46:47.680 keeping in mind we're projecting forward a few minutes because 0:46:47.880 --> 0:46:52.320 the information we have is older. And then, knowing that 0:46:52.680 --> 0:46:56.919 our ability to pinpoint a spacecraft position with precision decreases 0:46:57.400 --> 0:47:00.120 the further out the spacecraft gets from us, we have 0:47:00.200 --> 0:47:02.879 to start building in margins of error, and then, based 0:47:02.960 --> 0:47:06.560 upon all we know, where is it heading to now 0:47:06.760 --> 0:47:09.560 and how can we get it back on track? If 0:47:09.640 --> 0:47:12.800 we were not able to determine this, we wouldn't know 0:47:13.360 --> 0:47:16.040 where to point the antenna with the d s N 0:47:16.560 --> 0:47:20.239 in order to track the spacecraft. We would lose the spacecraft, 0:47:20.840 --> 0:47:23.440 let alone being able to figure out how to correct 0:47:23.680 --> 0:47:27.360 its its course. And you know space is big, so 0:47:27.560 --> 0:47:30.480 if you lose something like a spacecraft, good luck finding 0:47:30.520 --> 0:47:34.920 it again, because you'd you'd just be scanning regions of 0:47:35.040 --> 0:47:38.520 space looking for the faintest of radio signals to try 0:47:38.600 --> 0:47:41.480 and get back on track. It's not something you want 0:47:41.560 --> 0:47:44.399 to have happen. Well, we've got some more to talk 0:47:44.480 --> 0:47:48.480 about with navigation before we wrap all this up, So 0:47:48.640 --> 0:47:59.279 let's take one last break. Okay, I was talking about 0:47:59.440 --> 0:48:02.719 orbit re construction before the break, and we also need 0:48:02.800 --> 0:48:05.320 to reconstruct the path of the spacecraft in order to 0:48:05.400 --> 0:48:08.759 make sure that the scientific data that we're collecting with 0:48:08.840 --> 0:48:11.640 this satellite. I mean, presumably we've sent it up there 0:48:11.680 --> 0:48:16.799 to do something, well, some of it is determined by 0:48:17.400 --> 0:48:20.080 the trajectory path, Like we have to know the trajectory 0:48:20.200 --> 0:48:23.000 path in order for the data to make sense. There's 0:48:23.080 --> 0:48:26.080 imaging data. There's like a type of imaging called synthetic 0:48:26.239 --> 0:48:29.719 aperture radar imaging, and that requires that we have a 0:48:29.880 --> 0:48:34.960 precise knowledge of the spacecraft's trajectory so that the software 0:48:35.040 --> 0:48:39.280 we use to process that information can create a meaningful 0:48:39.440 --> 0:48:43.160 image from that data. Like it's not like it's sending 0:48:43.200 --> 0:48:45.719 a JPEG to us. It's sending us data that we 0:48:46.080 --> 0:48:50.840 then use to create an image with sophisticated software we 0:48:50.880 --> 0:48:53.839 have running on computers here on Earth. If we don't 0:48:53.920 --> 0:48:57.320 know the trajectory precisely, then it's almost like we're building 0:48:57.360 --> 0:48:59.719 a picture, but we're doing it from the wrong perspective, 0:48:59.840 --> 0:49:02.080 and it would leave us with an image that's nothing 0:49:02.200 --> 0:49:05.520 like what we were actually trying to capture with the satellite. 0:49:05.920 --> 0:49:11.480 So it is imperative that we know the actual trajectory 0:49:11.600 --> 0:49:15.800 of a spacecraft. Then we have flight path control, the 0:49:15.960 --> 0:49:19.200 third of the three departments I was talking about. Again, 0:49:19.280 --> 0:49:21.520 you could probably guess what this is about based on 0:49:21.600 --> 0:49:24.560 the name. We can summarize this by saying that this 0:49:24.960 --> 0:49:28.120 is the part of space navigation where we figure out 0:49:28.239 --> 0:49:31.440 how to get the spacecraft from where it actually is 0:49:32.120 --> 0:49:34.880 to where it is supposed to be. How can you 0:49:34.960 --> 0:49:39.160 get the spacecraft to return to the reference trajectory that 0:49:39.520 --> 0:49:42.239 you had set in the beginning. And here's another good 0:49:42.320 --> 0:49:46.200 reason to put so much emphasis on orbit determination, because 0:49:46.239 --> 0:49:49.000 spacecraft have a very limited set of options that they 0:49:49.080 --> 0:49:51.760 can use in order to return to the correct course. 0:49:52.320 --> 0:49:57.160 An interplanetary spacecraft, like a satellite that's designed to fly by, say, 0:49:57.640 --> 0:50:01.200 one of Saturn's moons, it needs to on course once 0:50:01.239 --> 0:50:04.200 it separates from the launch vehicle. You know, once it 0:50:04.360 --> 0:50:07.680 separates from the rocket that pushes it up into space. 0:50:08.440 --> 0:50:11.200 So this is kind of like a bowler releasing a 0:50:11.320 --> 0:50:14.120 bowling ball. You know, once that ball leaves your hand, 0:50:14.920 --> 0:50:18.040 there ain't no amount of you waving or leaning that's 0:50:18.080 --> 0:50:21.200 really going to affect the ball's trajectory. You've set it 0:50:21.280 --> 0:50:25.000 on a path and you can't really influence it anymore. Well, 0:50:25.600 --> 0:50:30.600 we can still influence spacecraft a little bit, but that 0:50:31.040 --> 0:50:35.719 initial release from the launch vehicle is the primary thing 0:50:35.800 --> 0:50:39.920 of putting it on its proper trajectory. So spacecraft can 0:50:39.960 --> 0:50:42.800 have like thrusters or rocket engines that can fire to 0:50:42.880 --> 0:50:45.680 adjust their course a little bit. But obviously there's actually 0:50:45.680 --> 0:50:49.040 a limit to how much fuel any spacecraft is able 0:50:49.080 --> 0:50:52.280 to carry. And there ain't no gas stations in space, 0:50:52.760 --> 0:50:55.640 at least not in our neighborhood. So fuel is a 0:50:55.760 --> 0:51:00.120 limited resource. And that's you know, an understatement, but it's 0:51:00.120 --> 0:51:04.080 important to remember. So let's say a spacecraft has gone 0:51:04.200 --> 0:51:07.000 a little bit off course. The flight path control group 0:51:07.080 --> 0:51:10.320 then has to figure out how far off course is it. 0:51:10.719 --> 0:51:13.120 Then they have to figure out the commands needed to 0:51:13.320 --> 0:51:16.560 have the spacecraft returned to its reference trajectory. So they 0:51:16.600 --> 0:51:20.160 take the data from the orbit determination group that tells them, okay, 0:51:20.360 --> 0:51:22.959 how far off course are we. Then they start running 0:51:22.960 --> 0:51:25.040 the calculations how much is it going to take for 0:51:25.160 --> 0:51:27.600 us to get back to where we need to be? Uh? 0:51:27.920 --> 0:51:30.560 This means figuring out the proper change in velocity for 0:51:30.719 --> 0:51:33.120 the spacecraft and if it's been a while since you've 0:51:33.160 --> 0:51:36.080 had physics, I want to remind you that velocity isn't 0:51:36.280 --> 0:51:39.600 just speed. A lot of folks use the word velocity 0:51:39.800 --> 0:51:42.800 to stand in for speed, but that's just part of it. 0:51:42.960 --> 0:51:46.400 Velocity is a vector. So in addition to speed, we 0:51:46.520 --> 0:51:49.360 have to have a direction. So a change in velocity 0:51:49.840 --> 0:51:52.080 is an acceleration. It can be a change in speed 0:51:52.600 --> 0:51:56.800 or direction or both. The flight path control team figures 0:51:56.800 --> 0:52:00.680 out what change in velocity is necessary, so they indicate 0:52:00.760 --> 0:52:04.000 the magnitude and the direction that is required in order 0:52:04.080 --> 0:52:07.680 for the spacecraft to return to its reference trajectory. Now, 0:52:07.760 --> 0:52:10.880 the flight path control team doesn't initiate the actual maneuver. 0:52:11.400 --> 0:52:14.040 They just designed the maneuver, or at least they design 0:52:14.120 --> 0:52:17.200 the parameters of the maneuver. It needs to have this 0:52:17.440 --> 0:52:21.200 change in direction and this magnitude. They send that information 0:52:21.400 --> 0:52:25.200 to another team, a spacecraft engineering team, and it's this 0:52:25.320 --> 0:52:28.680 group that then use stuff like attitude control systems and 0:52:28.840 --> 0:52:32.560 thrusters or rocket engines to produce the change in velocity 0:52:32.680 --> 0:52:35.520 that was indicated by the flat flight path control teams. So, 0:52:35.520 --> 0:52:38.200 in other words, they're the ones to take this data 0:52:38.719 --> 0:52:41.360 that says, here's what we need to have happen, and 0:52:41.400 --> 0:52:44.040 they're the ones to actually activate the systems to make 0:52:44.080 --> 0:52:47.760 it happen. NASA refers to small flight path control maneuvers 0:52:48.120 --> 0:52:52.200 as trajectory correction maneuvers, which makes sense. You're trying to 0:52:52.239 --> 0:52:55.879 correct it move it back to its reference trajectory. Now, 0:52:56.239 --> 0:52:59.200 as we conduct more space exploration, we learned things that 0:52:59.280 --> 0:53:02.520 are really able for future missions. So, for example, if 0:53:02.600 --> 0:53:04.640 we were to plot out a fly by satellite to 0:53:04.680 --> 0:53:08.839 go to Saturn, we would incorporate some gravity assist fly by. 0:53:08.880 --> 0:53:12.000 It's most likely this is where you leverage the gravitational 0:53:12.120 --> 0:53:16.880 pull of celestial body like another planet, to assist the 0:53:17.000 --> 0:53:18.920 spacecraft on its way by giving it kind of a 0:53:19.000 --> 0:53:23.279 slight pull slash push towards its destination and a change 0:53:23.280 --> 0:53:26.560 in velocity. It's a boost, kind of like someone giving 0:53:26.600 --> 0:53:28.799 you a little push when you're swinging on a swing set, 0:53:28.960 --> 0:53:32.280 although it can also you know, change your direction somewhat. 0:53:32.560 --> 0:53:35.160 And as we understand these things and we're able to 0:53:35.239 --> 0:53:38.920 build it in, we can have that planned from the beginning, 0:53:39.120 --> 0:53:42.960 so we can build them into an actual mission. When 0:53:43.000 --> 0:53:45.600 we've got a good handle on those things, NASA can 0:53:45.680 --> 0:53:48.319 call any sort of velocity maneuvers that we know we're 0:53:48.360 --> 0:53:52.480 going to have to do deterministic. That is, we have 0:53:52.560 --> 0:53:56.320 already determined the velocity maneuvers that we will need to 0:53:56.840 --> 0:54:01.239 conduct in order to maintain our reference true jectory given 0:54:01.280 --> 0:54:04.200 the route that we're following. We know that they are 0:54:04.280 --> 0:54:07.440 going to be maneuvers necessary to stay on course, and 0:54:07.520 --> 0:54:10.440 we have a good idea of what they are and 0:54:10.600 --> 0:54:13.120 when we will need to execute them. But there are 0:54:13.160 --> 0:54:17.279 other types of maneuvers that will call stochastic. These are 0:54:17.360 --> 0:54:20.360 maneuvers that we know we're gonna need to make, but 0:54:20.520 --> 0:54:23.320 we don't necessarily know. More like, we don't know what 0:54:23.520 --> 0:54:26.719 the magnitude of those changes might have to be. We 0:54:26.920 --> 0:54:30.440 might not fully understand the effect of those maneuvers ahead 0:54:30.480 --> 0:54:35.040 of time, because we're going through uncharted ground, if you 0:54:35.320 --> 0:54:38.279 if you will. We're not following something that we've already done, 0:54:38.360 --> 0:54:41.200 where we already kind of have a grasp on what 0:54:41.400 --> 0:54:44.640 we need to do. And then, of course occasionally sometimes 0:54:44.680 --> 0:54:46.840 we have to do these maneuvers when something we didn't 0:54:46.840 --> 0:54:50.040 anticipate at all happens and we have to design and 0:54:50.200 --> 0:54:54.120 conduct a maneuver kind of on demand. Also, I should 0:54:54.160 --> 0:54:58.080 mention that attitude control I mentioned it earlier Attitude control 0:54:58.360 --> 0:55:01.320 is not about whether or not you're spacecraft is sassin you. 0:55:02.160 --> 0:55:05.360 It has nothing to do with sass. Attitude refers to 0:55:05.520 --> 0:55:09.480 the angular orientation of a spacecraft given some other point 0:55:09.480 --> 0:55:12.160 of reference. Again, you have to have a point of reference, 0:55:12.760 --> 0:55:16.280 because I mean, if you think about it, outer space 0:55:16.320 --> 0:55:19.400 doesn't really have an up or down. You have to 0:55:19.440 --> 0:55:23.360 have a point of reference and compare your position to 0:55:23.600 --> 0:55:26.400 that point of reference, or you have to, you know, 0:55:26.560 --> 0:55:28.279 use your point of reference to in order to make 0:55:28.520 --> 0:55:32.440 a determination about something's positions. So you've gotta have a 0:55:32.520 --> 0:55:34.279 point of reference to start from in order for you 0:55:34.360 --> 0:55:37.200 to say something like that durned things upside down or 0:55:37.280 --> 0:55:41.480 backwards or you know, or whatever. Also, there are interesting 0:55:41.560 --> 0:55:45.719 ways to change the angular orientation of a spacecraft, and 0:55:45.880 --> 0:55:49.760 some of them do not involve thrusters or rocket engines. Instead, 0:55:49.840 --> 0:55:54.040 they might involve something like momentum wheels, as in, you know, 0:55:54.280 --> 0:55:58.719 physical wheels a rotor spun by a motor. Now I 0:55:58.719 --> 0:56:02.280 would get into this further, but that requires a pretty 0:56:02.400 --> 0:56:05.480 long discussion about things like the conservation of momentum and 0:56:05.719 --> 0:56:08.360 equal and opposite reactions and stuff like that, and we 0:56:08.640 --> 0:56:11.200 don't really have time for that this episode. Is already 0:56:11.239 --> 0:56:13.840 going super long, and I don't want Tardy to hate 0:56:13.880 --> 0:56:19.240 me more than she does already. So she doesn't hate me, folks, 0:56:19.400 --> 0:56:21.040 She's super nice to me. I just want to make 0:56:21.080 --> 0:56:23.840 that clear. That was more of a jest. But the 0:56:24.239 --> 0:56:27.160 short version of all this is that using stuff like 0:56:27.280 --> 0:56:30.759 momentum wheels can make it possible to change the attitude 0:56:30.880 --> 0:56:34.120 of a spacecraft without having to use thrusters. And as 0:56:34.200 --> 0:56:38.640 we've previously established, fuel is a precious resource. So that's 0:56:38.680 --> 0:56:41.400 a good thing to know, right to build in systems 0:56:41.680 --> 0:56:45.600 that allow us to make changes to a spacecraft's orientation, 0:56:45.719 --> 0:56:49.600 for example, without having to burn fuel to do it. Still, 0:56:50.000 --> 0:56:53.240 it's not uncommon that the spacecraft engineering team will actually 0:56:53.320 --> 0:56:56.280 have to initiate a rocket engine or a thruster ignition 0:56:56.680 --> 0:56:59.840 to provide the thrust needed to get back onto the 0:57:00.040 --> 0:57:03.640 reference trajectory. Uh, the timing on these maneuvers has to 0:57:03.719 --> 0:57:07.520 be incredibly precise, both because you don't want to waste 0:57:07.600 --> 0:57:09.680 even a drop of fuel if you can help it, 0:57:10.239 --> 0:57:13.359 and also that if you fire a thruster for too 0:57:13.440 --> 0:57:15.520 long or not long enough, then you're not going to 0:57:15.600 --> 0:57:19.320 return to your reference trajectory. So imagine, for a moment 0:57:19.360 --> 0:57:23.200 that you're sitting in mission control and you are relying 0:57:23.320 --> 0:57:27.640 on complex calculations from data sent back to you from 0:57:27.800 --> 0:57:32.200 space just to tell you where that something is right, 0:57:32.680 --> 0:57:35.880 and that's something the spacecraft is so far away that 0:57:36.000 --> 0:57:38.560 there is no means for us to observe it directly. 0:57:38.800 --> 0:57:41.600 All you have is the data coming back to go by, 0:57:42.400 --> 0:57:44.360 and then you have to come up with the command 0:57:44.760 --> 0:57:48.560 to send via radio back up to this object to 0:57:48.680 --> 0:57:50.880 get it back onto the course it's supposed to be 0:57:50.960 --> 0:57:54.320 following the data you have indicates that the thing you 0:57:54.400 --> 0:57:57.840 know was in this one particular position several minutes ago, 0:57:58.160 --> 0:57:59.880 So you have to figure out where it is now 0:58:00.520 --> 0:58:04.640 based on calculations with the data that you have, knowing 0:58:05.000 --> 0:58:09.240 that that is at best maybe a precise approximation, but 0:58:09.320 --> 0:58:12.320 still an approximation. Then you figure out the command you 0:58:12.400 --> 0:58:15.120 need to send to where the spacecraft is going to 0:58:15.280 --> 0:58:18.680 be in order to get it to take the action 0:58:18.960 --> 0:58:22.080 to get it to where it should be. This whole 0:58:22.160 --> 0:58:25.439 thing is mind boggling to me. It kind of makes 0:58:25.480 --> 0:58:29.680 me think of like submarine navigators who use precise charts 0:58:30.200 --> 0:58:33.440 and timing like a stop watch in order to plot 0:58:33.600 --> 0:58:37.560 underwater courses. Because they're not able to just look outside. 0:58:37.640 --> 0:58:40.840 I mean, at the depths that submarines can travel. You 0:58:40.920 --> 0:58:44.560 can't have windows because they would collapse in from the pressure. 0:58:45.040 --> 0:58:50.520 So you're in a tin can underwater, and you're using 0:58:51.200 --> 0:58:54.880 very precise maps and a stopwatch and knowledge of how 0:58:55.000 --> 0:58:58.600 fast you're moving in order to make calculations to determine 0:58:58.640 --> 0:59:01.080 whether or not you're going to bump into something. It's 0:59:01.880 --> 0:59:05.800 hard for me to even contemplate. Well, once the spacecraft 0:59:05.840 --> 0:59:09.480 engineering team has done their thing, that whole process has 0:59:09.520 --> 0:59:12.160 to repeat itself. The orbit determination team has to figure 0:59:12.160 --> 0:59:14.880 out if the spacecraft is in fact back on its 0:59:14.960 --> 0:59:19.080 reference trajectory, or if they'll need to conduct another maneuver, 0:59:19.600 --> 0:59:22.000 and so on and so forth. And because there's so 0:59:22.120 --> 0:59:25.919 many little things that can pull a spacecraft off track, 0:59:26.360 --> 0:59:31.840 this becomes a continuous process. It's incredible to me that 0:59:31.960 --> 0:59:34.480 people figured this stuff out, that they figured out how 0:59:34.600 --> 0:59:37.640 to not just not just how the universe works, Like 0:59:37.680 --> 0:59:40.880 it's already incredible to me that Einstein was able to 0:59:41.000 --> 0:59:46.160 determine these in incredible theories of special and general relativity, 0:59:46.600 --> 0:59:49.360 but then for people to build on that and to 0:59:49.440 --> 0:59:54.240 make technologies that take that into account, it's it's phenomenal. 0:59:54.320 --> 0:59:57.240 It also tells you by the way science works, right, 0:59:57.560 --> 1:00:01.280 because if science didn't work, the technology we build that 1:00:02.200 --> 1:00:07.040 leverages that science, it wouldn't work. So science works or 1:00:07.120 --> 1:00:09.840 else are tech wouldn't work, especially when it comes to 1:00:09.880 --> 1:00:12.760 space navigation. Now, there is a lot more that we 1:00:12.800 --> 1:00:16.080 could say about spacecraft navigation. I haven't really gone into 1:00:16.360 --> 1:00:21.280 deep details here, uh like how do you determine what 1:00:21.360 --> 1:00:24.400 a spacecraft's velocity is? For example? I haven't talked about 1:00:24.440 --> 1:00:27.920 that process, but I felt this was a good if 1:00:27.960 --> 1:00:31.280 you will high level overview of the topic. If you 1:00:31.320 --> 1:00:34.919 would like to know more details, let me know. I'll 1:00:35.200 --> 1:00:38.000 research and write and do a follow up episode and 1:00:38.160 --> 1:00:40.400 it will reference this one, but it will go into 1:00:40.480 --> 1:00:43.680 much more detail to talk about the actual processes and 1:00:43.760 --> 1:00:46.400 technologies we use to do the things I've talked about 1:00:46.480 --> 1:00:49.520 in this episode. If you want that episode or any 1:00:49.600 --> 1:00:52.760 other topic on tech Stuff, reach out to me on Twitter. 1:00:52.920 --> 1:00:54.200 That's the best way to get in touch with me. 1:00:54.640 --> 1:00:57.120 The handle we use for the show is tech Stuff 1:00:57.520 --> 1:01:03.000 H s W and I'll talk to you again really soon. Yeah. 1:01:07.080 --> 1:01:10.080 Text Stuff is an I Heart Radio production. For more 1:01:10.200 --> 1:01:13.560 podcasts from I Heart Radio, visit the I heart radio, app, 1:01:13.680 --> 1:01:16.840 Apple podcasts, or wherever you listen to your favorite shows.